Islets

3-D perspective view of the southeastern Hawaiian Islands, with the white summits of Mauna Loa (4,170 m or 13,680 ft high) and Mauna Kea (4,206 m or 13,799 ft high). The islands are the tops of massive volcanoes, the bulk of which lie below the sea surface. Ocean depths are colored from violet (5,750 m or 18,860 ft deep northeast of Maui) and indigo to light gray (shallowest). Historical lava flows are shown in red, erupting from the summits and rift zones of Mauna Loa, Kilauea, and Hualalai volcanoes on Hawaiʻi.

The state of Hawaii counts 137 "islands" in the Hawaiian chain.[14] This number includes all minor islands and islets offshore of the main islands (listed above) and individual islets in each atoll. These are just a few:

A composite satellite image from NASA of the Hawaiian Islands taken from outer space. Click on the image for a larger view that shows the main islands and the extended archipelago.

Geology

The chain of islands or archipelago formed as the Pacific plate moved slowly northwestward over a hotspot in the Earth's mantle at about 32 miles (51 km) per million years. Hence the islands in the northwest of the archipelago are older and typically smaller, due to longer exposure to erosion. The age of the archipelago has been estimated using potassium-argon dating methods.[15] From this study and others,[16][17] it is estimated that the northwestern most island, the Kure Atoll, is the oldest at approximately 28 million years (Ma); while the southeastern most island, Hawaiʻi, is approximately 0.4 Ma (400,000 years). The Hawaiian islands are right on top of a hot spot which makes it full of volcanoes and such.The only active volcanism in the last 200 years has been on the southeastern island, Hawaiʻi, and on the submerged but growing volcano at the extreme southeast, Loʻihi. The Hawaiian Volcano Observatory of the U. S. Geological Survey documents recent volcanic activity and provides images and interpretations of the volcanism.

Almost all magma formed in the hotspot has the composition of basalt, and so the Hawaiian volcanoes are constructed almost entirely of this igneous rock. There is very little coarser grained, gabbro and diabase. Nephelinite, does occur on the islands but is extremely rare. The majority of eruptions in Hawaiʻi are Hawaiian-type eruptions because basaltic magma is relatively fluid compared with magmas typically involved in more explosive eruptions, such as the andesitic magmas that produce some of the spectacular and dangerous eruptions around the margins of the Pacific basin.

Hawaiʻi island (the Big Island) is the biggest and youngest island in the chain, built from five volcanoes. Mauna Loa, taking up over half of the Big Island, is the largest shield volcano on the Earth. The measurement from sea level to summit is more than 2.5 miles (4 km), from sea level to sea floor about 3.1 miles (5 km).[18]

Earthquakes

The Hawaiian Islands have many earthquakes, generally caused by volcanic activity. Most of the early earthquake monitoring took place in Hilo, by missionaries Titus Coan, Sarah J. Lyman and her family. From 1833 to 1896, approximately 4 or 5 earthquakes were reported per year.[19]

Hawaii accounted for 7.3% of the United States' reported earthquakes with a magnitude 3.5 or greater from 1974 to 2003, with a total 1533 earthquakes. Hawaii ranked as the state with the third most earthquakes over this time period, after Alaska and California.[20]

On Sunday, October 15, 2006, there was an earthquake with a magnitude of 6.7 off the northwest coast of the island of Hawaii, near the Kona area of the big island. The initial earthquake was followed approximately five minutes later by a magnitude 5.7 aftershock. Minor-to-moderate damage was reported on most of the Big Island. Several major roadways became impassable from rock slides, and effects were felt as far away as Honolulu, Oahu, nearly 150 miles (240 km) from the epicenter. Power outages lasted for several hours to days. Several water mains ruptured. No deaths or life-threatening injuries were reported.

Tsunamis

Aftermath of the 1960 Chilean tsunami in Hilo, Hawaiʻi, where the tsunami left 61 people dead and 282 seriously injured. The waves reached 35 feet (11 m) high.

The Hawaiian Islands are subject to tsunamis, great waves that strike the shore. Tsunamis are most often caused by earthquakes somewhere in the Pacific. The waves produced by the earthquakes travel at speeds of 400–500 miles per hour (600–800 km/h) and can affect coastal regions thousands of miles (kilometers) away.

Tsunamis may also originate from the Hawaiian Islands. Explosive volcanic activity can cause tsunamis. The island of Molokaʻi had a catastrophic collapse or debris avalanche over a million years ago; this underwater landslide likely caused tsunamis. The Hilina Slump on the island of Hawaiʻi is another potential place for a large landslide and resulting tsunami.

The city of Hilo on the Big Island has been most affected by tsunamis, where the in-rushing water is accentuated by the shape of Hilo Bay. Coastal cities have tsunami warning sirens.

A tsunami resulting from an earthquake in Chile hit the islands on February 27, 2010. It was relatively minor, but local emergency management officials utilized the latest technology and ordered evacuations in preparation for a possible major event. It was declared a "good drill" for the next major event by the Governor.

A tsunami resulting from an earthquake in Japan hit the islands on March 11, 2011. It was relatively minor, but local officials ordered evacuations in preparation for a possible major event. The tsunami caused about $1 million in damages, almost all limited to the Kona coast of the Big Island. However, due to the deep underwater trenches that surround the Hawaiian islands, very few tsunamis reach them.

Ecology

The endemic plant and animal species of the Hawaiian Islands developed in nearly complete isolation over about 70 million years. Prior to the human arrival, the only native mammals were the Hawaiian hoary bat and the Hawaiian monk seal.[21]

Human contact, first by Polynesians, introduced new trees, other plants and animals. These included voracious species such as rats and pigs, who took a heavy toll on native birds and invertebrates that evolved in the absence of such predators. The growing population also brought deforestation, forest degradation, treeless grasslands, and environmental degradation. As a result, many species which depended on forest habitats and food went extinct. As humans cleared land for farming, monocultural crop production replaced multi-species systems.

The arrival of the Europeans had a more significant impact, with the promotion of large-scale single-species export agriculture and livestock grazing. This led to increased clearing of forests, and the development of towns, adding many more species to the list of extinct animals of the Hawaiian Islands. As of 2009, many of the remaining endemic species are considered endangered.[22]

National Monument

On June 15, 2006, President Papahānaumokuākea Marine National Monument under the Antiquities Act of 1906. The Monument encompasses the northwestern Hawaiian Islands and surrounding waters, forming the largest marine wildlife reserve in the world.

Climate

The climate of the Hawaiian Islands is tropical but it experiences many different climates, depending on altitude and weather.[23] The islands receive most rainfall from the trade winds on their north and east flanks (the windward side) as a result of orographic precipitation.[23] Coastal areas in general and especially the south and west flanks or leeward sides, tend to be drier.[23]

In general, the lowlands of Hawaiian Islands receive most of their precipitation during the winter months (October to April).[23] Drier conditions generally prevail from May to September.[23] The tropical storms, and occasional hurricanes, tend to occur from July through November.[23]

^"Tectonics, geochronology, and origin of the Hawaiian-Emperor Volcanic Chain". The Geology of North America, Volume N: The Eastern Pacific Ocean and Hawaii. The Geology Society of America. 1989. Retrieved 2011-01-17.

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